Is it actually running that long? Do you see the process running on your server? Or does it hang, and get reset after 6 hours? I would suggest disabling your cron job, and enabling error reporting and debugging and running it manually when it's scheduled to run next.
To enable error reporting, edit /config/blesta.php and change **Configure::errorReporting(0);** to **Configure::errorReporting(-1);** You may also wish to enable System Debug. To do so, change **Configure::set("System.debug", false);** to **Configure::set("System.debug", true);**
It's a good idea to change these settings back when you are done.